Permanently joined plate heat exchangers are used to an increasing extent. The joining together may be done by brazing but also welding and gluing are used. At a pressure overloading a permanently joined plate heat exchanger leakage will arise and the leakage is generally located to the port areas and/or the circumferential areas of the heat exchanging plates in connection to the inlet and outlet channels. The plate heat exchanger has within the port areas of the plates relatively large projected areas without connecting joints between the heat exchanging plates. Upon these areas forces from pipe loads and fluid pressure are acting. The joints which are situated closest to the port areas of the plates run the risk of being over-loaded and torn up.
U.S. Pat. No. 5,462,113 shows a plate heat exchanger for three fluids. The heat exchanger comprises a core of plates with heat exchanging plates, end plates and inlet devices and outlet devices for the heat exchanging fluids. The attachment of the end plate 12 to the extra sealing plate 16 is wide in comparison with the port channel for the heat exchanging fluid R1 and will probably contribute to an increased resistance to pressure load. The resistance may still be improved.